Stabilization of methylmethacrylate-butadiene-styrene graft copolymers against thermal oxidation

Abstract

The instant invention relates to a stabilized composition of methylmethacrylate-butadiene-styrene graft copolymers with selected sterically hindered phenolic antioxidants and thioethers. Further subjects of the invention are a process for the stabilization of methylmethacrylate-butadiene-styrene graft copolymers and the use of selected sterically hindered phenolic antioxidants together with a thioether for the thermal stabilization of said graft copolymer.

1 . A stabilized polymer composition comprising
 a) a polymer, which is a graft copolymer of methylmethacrylate and styrene on polybutadiene or on polybutadiene-styrene (methylmethacrylate-styrene-butadiene graft copolymer, MBS);   b) a sterically hindered phenolic antioxidant of formula (I), (II) or (III) or a mixture thereof   
     
       
         
         
             
             
         
       
     
     wherein n is from 1-10; 
     
       
         
         
             
             
         
       
     
     and
 c) a thioether differing from that of formula (II); 
 
     with the proviso that other styrene/polybutadiene graft copolymers are not present. 
   
   
       2 . A stabilized polymer composition according to  claim 1 , which is in the solid state. 
   
   
       3 . A stabilized polymer composition according to  claim 2 , which is in the form of a powder or granulate. 
   
   
       4 . A stabilized polymer composition according to  claim 1  wherein the thioether is a compound of formula (IV) or (V) 
     
       
         
         
             
             
         
       
     
     wherein the R 1  are independently C 8 -C 20 alkyl. 
   
   
       5 . A stabilized polymer composition according to  claim 1  wherein the sterically hindered phenolic antioxidant is present in an amount of 0.05 to 1% based on the weight of the dry graft copolymer, component a). 
   
   
       6 . A stabilized polymer composition according to  claim 1  wherein the thioether is present in an amount of 0.1 to 5% based on the weight of the dry graft copolymer, component a). 
   
   
       7 . A stabilized polymer composition according to  claim 1  wherein the ratio of sterically hindered phenolic antioxidant to thioether is from 1:1 to 1:5. 
   
   
       8 . A stabilized polymer composition according to  claim 1  additionally comprising a further sterically hindered phenolic antioxidant different from that of  claim 1 , a phosphite process stabilizer, a UV-absorber, a sterically hindered amine light stabilizer, a metal deactivator, an acid scavenger, a metal salt of a fatty acid, a fluorescent whitening agent, a biocide or a surfactant. 
   
   
       9 . A process for the stabilization of a graft copolymer of methylmethacrylate and styrene on polybutadiene or polybutadiene-styrene (methylmethacrylate-styrene-butadiene graft copolymer, MBS) where no other styrene polymer or copolymer, which is not a graft copolymer on butadiene is present, comprising the steps
 a) adding to a MBS latex a sterically hindered phenolic antioxidant of formula (I), (II) or (III);   
     
       
         
         
             
             
         
       
     
     wherein n is from 1-10; 
     
       
         
         
             
             
         
       
     
     and a thioether differing from that of formula (II);
 b) coagulating the MBS latex and 
 c) drying the MBS latex at elevated temperature. 
 
   
   
       10 . A process according to  claim 9  wherein the drying step is carried out at a temperature of 40° C. to 150° C.